1. Field of the Invention
The present invention relates to a magnetic disk device, and particularly to a magnetic disk device and a retry method for a magnetic disk device that changes the content of retry processing according to the access state of commands from a host device.
2. Description of the Related Art
In the prior art, a magnetic disk device reads or records with respect to a series of sectors on a magnetic medium upon receiving a read/write command from a host computer. However, when the magnetic disk device encounters sectors that, for whatever reason, cannot be read from or recorded to, it again attempts to read from or record to the sector in which the error occurred.
Regarding the method of retry, the magnetic disk device, for example, reads from or records to the sector in which an error occurred a stipulated limited number of times, and if reading or recording is successful within this number of times, the magnetic disk device regards this as normal reading or recording and continues reading from or recording to the next sector.
As another retry method, the magnetic disk device does not merely read from or record to a sector in which an error has occurred, but adds another process. For example, when reading, the magnetic disk device reads again after slightly shifting the position of the head in a direction toward or away from the disk center. Alternatively, the magnetic disk device retries reading while, for example, changing the gain of the amplifier that amplifies the output voltage of the head.
When actually executing a retry, the retry process of the magnetic disk device is executed by a particular set procedure, the series of retry operations being terminated when the retry is successful.
In the above-described retry method of the prior art, however, there is the problem that when executing the retry processing, the magnetic disk device fails to send the data requested by the host computer within a stipulated time period. A particularly short data transfer time is demanded of a magnetic disk device used in an active image processing system. In a retry method of the prior art, however, the initiation of the retry process interrupts the active image data transfer of the active image processing system, giving rise to disturbances or interruptions in the active image.
In the retry method of the prior art, a magnetic disk device can lighten the retry processing to prevent interruptions in data transfer. However, the magnetic disk device in such a case must lighten the retry processing in all cases, and therefore may fail to execute sufficient retry processing even when there is plenty of time for it, thereby increasing the frequency of error generation. Magnetic disk devices used in active image processing systems therefore cause disturbances in the active image.
It is an object of the present invention to provide a magnetic disk device and a magnetic disk device retry method that can suppress interruptions in data transfer to a minimum and that allows the most effective retry processing within the range that suppresses interruptions to a minimum so as to solve the above-described problems.
It is another object of the present invention to provide a magnetic disk device and a magnetic disk device retry method that suppresses drops in the throughput of the magnetic disk device and prevents the occurrence of errors or interruptions in data transfer.
The magnetic disk device of the present invention comprises: a driving means (5) that includes a magnetic disk-shaped medium and that drives the magnetic disk-shaped medium-shaped medium; reading/writing means (7) that includes error detecting means (8) and that reads or writes data; positioning means (6) for determining the position of the reading/writing means on the magnetic disk; interface control means (1) for communicating with the host computer; command queue (2) for storing commands received in the interface control means; load detecting means (3) for detecting the load of interface with the host computer based on the total number of commands stored in the command queue; load level conversion table (10) that takes the number of commands stored in the command queue as the-index value; retry table (9) for storing in advance contents of retry processing that correspond to the load levels of the load detecting means; and executing means (4) for fetching and executing commands from the command queue, and when retry is necessary, for obtaining the content of retry processing that corresponds to a load level detected by the load detecting means and executing the retry process.
The magnetic disk device of the present invention thus takes the total number of commands stored in the command queue as the load level of the interface with the host computer. When a retry is necessary, the magnetic disk device thus obtains from the retry table the content of retry processing that corresponds to the load level detected by the load detecting means and executes retry processing.
In addition, the retry table (9) is produced while establishing a correspondence between interface loads and contents of retry processing such that heavy retry processing is performed when the interface load is light and light retry processing is performed when the interface load is heavy. The magnetic disk device of the present invention performs heavy retry processing when there are few queued commands and light retry processing when there are many commands using a correlation in which the demand for data transfer processing increases in proportion to the number of commands previously issued from the host computer (the number of queued commands), and thus always selects the optimum retry processing for the load from the host computer.
The executing means (4) refers to the retry table each time retry is carried out with respect to a same sector on the medium and obtains from the retry table a content of retry processing that corresponds to the load level at that time.
According to the retry method of the present invention, the magnetic disk device: receives commands from the host computer by the interface control means; stores the commands received by the interface control means in the command queue; detects the load of the interface with the host computer based on the total number of commands stored in the command queue; fetches and executes commands from the command queue and, when a retry is necessary, obtains from the retry table a content of retry processing that corresponds to the detected load level and executes retry processing.
In addition, interface loads and contents of retry processing are stored in the retry table with a correspondence such that heavy retry processing is performed when the above-described interface load is light and light retry processing is performed when the load is heavy.
Furthermore, the retry table is consulted each time a retry is executed with respect to the same sector on the medium, and a retry processing content that corresponds to the load level at that time is thus acquired from the retry table.
According to the present invention, when a retry is necessary, the magnetic disk device can reduce the amount of time spent for retry when the interface load is heavy by obtaining from the retry table a content of retry processing that corresponds to the detected load level and then executing the retry processing. As a result, a magnetic disk device that is used in an active image processing system can prevent interruptions in data transfer that interrupt and disrupt an active image.
In addition, the magnetic disk device can reduce the amount of time spent for a retry even in a case in which sectors in a plurality locations fail for one command because the magnetic disk device refers to the retry table and changes the content of retry processing each time an error occurs and retry becomes necessary.
The magnetic disk device can suppress interruptions in data transfer to a minimum and can execute the most effective retry processing within a limited time because interface loads and the contents of retry processing are stored in the retry table with a correspondence such that heavy retry processing is performed when the interface load is light and light retry processing is performed when the load is heavy.
Finally, the magnetic disk device can interrupt a retry when the load of interface increases and reduce the amount of time spent in a retry even during retry of the same sector because the magnetic disk device refers to the retry table and obtains from the retry table the content of retry processing that corresponds to the load level at that time each time retry is executed with respect to the same sector on the medium.
The above and other objects, features, and advantages of the present invention will become apparent from the following description based on the accompanying drawings which illustrate examples of preferred embodiments of the present invention.